In the combustion process of diesel engines, apart from water steam, nitrous oxides and carbon dioxides soot particles are also formed. In order to reduce the exhaust (release into the atmosphere) of soot particles, a particle trap can be arranged in the exhaust channel. The soot particles are caught in the particle trap, by means of which the exhaust gases are purified. As an example, EP 341 832 (equivalent to U.S. Pat. No. 4,902,487) describes a system having a filter in which soot particles are caught.
The soot particles are then incinerated in an ambience of nitrous dioxide. The nitrogen dioxide is formed from the exhaust gases from nitrogen monoxide in an oxidization catalyzer that is arranged upstream from the filter. A problem with the system described in is that its capacity for transforming the soot particles to carbon dioxide is low when operational conditions are producing low exhaust gas temperatures. This means that the regeneration of the particle filter will take too much time or, where applicable, will not be sufficient. This can lead to the filter gradually becoming blocked with an associated, increasing, fall in pressure as a consequence. This, in turn, means that the filter needs to be serviced often.